Electrically operated hoists or pulley blocks



June 11, 1968 A. T. c. BuRRows 3,387,822

ELECTRICALLY OPERATED HOISTS OR PULLEY BLOCKS Filed Feb. 9, 1967 2Sheets-Sheet l Junell, 1968 A. T. c. BURRows 3,387,822

v ELECTRICALLY OPERATED HOISTS OR PULLEY BLOCKS Filed Feb. 9, 1967 2Sheets-Sheet 2 3,387,822 ELECTRICALLY OPERATED HOISTS R PULLEY BLOCKSArthur Thomas Charles Burrows, Hertfordshire, Engl land, assignor toGeo. W. King Limited, Stevenage, "Hertfordshire, England, a Britishcompany Filed Feb. 9, 1967, Ser. No. 614,978 Claims priority,application Great Britain, Feb. 11, 1966, 6,247/66 3 Claims. (Cl.254-174) ABSTRACT 0F THE DISCLOSURE In an electrically operated hoist orpulley block incorporating a slipping clutch between the motor and thesprocket or winding drum the provision of at least one latch or pawldevice capable of movement into and out of an operative position whereinit will .positively -lock the sprocket or drum against rotation. Meansare provided for controlling the latch or pawl device so that whileduring a normal lifting or lowering movement it will be retainedinoperative, approach to the limit of travel of the hoist chain or cablein one direction or the other will result in movement of said latch orpawl device into its operative position. Resilient means are providedfor minimizing the shock on the hoist chain or cable as a result oflocking of the sprocket or drum.

This invention is concerned with electrically operated hoists or pulleyblocks and more particularly to such apparatus incorporating a loadlimiting or so-called slip- .ping clutch between the drive motor and theload sprocket or winding drum. The employment of a slipping clutch hasthe advantages that the electrical control system of the block can besimplied since it is no longer necessary to provide top and bottom limitswitches. Moreover a block so equipped is safer in use since it isimpossible to lift much more than the set working load and if the -loadhook becomes caught up in any way during a lifting operation the clutchwill slip. Again shock caused by careless operation of the block willalso be limited.

While the incorporation of a slipping clutch in a chain hoist or pulleyblock results, as indicated above, in a number of advantages there isone disadvantage and that is that the load chain or cable has towithstand at least twice the working load when the chain or cable islowered to its fullest extent and the slack end of the chain has towithstand the working load plus the force due to the slipping of theclutch. This is quite a serious matter since it means that the loadchain has to be appreciably larger than that required with earliercontrol systems, i.e., the blocks having no slipping clutch andincorporating top and bottom limit switches.

It is the primary object of the present invention to provide a mechanismwhich Will be effective to limit the maximum load in the chain so thatit will not materially exceed the set working load at any time during alowering operation. lt may be mentioned here that while that is aprimary object, the invention is however not limited solely to thecontrol of lowering operations but may well be employed for controllinglifting operations.

According to the present invention it is proposed in an electricallyoperated hoist or pulley Iblock incorporan ing a slipping clutch betweenthe driving motor and the load sprocket or winding drum, to providemeans adapted to be actuated as a result of a predetermined travel ofthe hoist chain or a predetermined winding of rope or cable oil or onthe drum, positively to engage the sprocket, drum or an elementassociated therewith thereby to lock said sprocket or drum againstfurther rotation.

States Patent The means may include one or a pair of pawls or likedevices which, or each of which is adapted to cooperate with a slot orrecess in the load sprocket, drum or an element associated therewith,the arrangement being such that while during normal operation the pawl(or both pawls where two are present) will be in an inoperative ordisengaged position, approach to the limit of travel of the chain in oneor either direction (or winding on or ott of a predetermined amount ofrope or cable) will result in movement of the pawl, or the appropriateone of such pawls into a position wherein it will engage the slot orrecess in the sprocket drum or element associated therewith.

In order that the said invention may be clearly understood and readilycarried into elect reference will now be made to the accompanyingdrawings in which:

FIGURE 1 shows in section a known type of electrically operated chainhoist or pulley block to which the invention is to be applied,

FIGURE 2 is a diagrammatic view illustrating the mechanism for limitingthe downward travel of the chain of a chain hoist, and

FIGURE 3 is a diagrammatic view illustrating a mechanism for limitingthe upward travel of the chain of a chain hoist.

Referring now to FlGURE l, 10 denotes a load or chain sprocket which isdriven by an electric motor 11 via a slipping clutch 12, a shaft 14 andgearing designated generally by 15. As is usual with hoists of this kinda brake assembly 16 is also incorporated.

As hereinbefore indicated the hoist illustrated in FIG- URE l is of aknown type and is shown merely as indicating one type of hoist to whichthe mechanism according to the invention may be applied.

Referring now to FIGURE 2, 10 again denotes the load or chain sprocketof a hoist or pulley block which in this case is provided, for example,by milling with a groove or recess 17 with which a sliding pawl 18 isadapted to cooperate. In FIGURE l a possible positioning of the grooveor recess 17 and of the pawl 18 is shown in dotted lines. In FIGURE 2the pawl 18 is shown in engagement with the groove or recess 17 butduring a normal lowering operation it will be displaced to the right andwill be clear of said groove or recess. The pawl 18 is located betweenguides 19 so as to be capable of free sliding movement which is impartedthereto by means of a sliding cam or actuating member 20. The member 20which cooperates with an inclined slot 18a in the pawl 18 is formed withan angled portion 20a, the arrangement being such that when themechanism is in the actuated position, as shown, and said member 20 isin its uppermost position, the pawl 18 will be in engagement with therecess 17 in the sprocket 10 while when said member 20 is in a -loweredposition, as it will be the Case during normal lowering operation, saidpawl 18 will, as a result of the shape of the member 20, be displaced tothe right out of engagement with the recess 17. The member 20 isslidably supported in guides 21 and is urged downwardly by a spring 22which bears against a stationary abutment 23. At its lower end themember 20 is provided with a pair of depending forks or extensions 24between which a bobbin like member 25 is freely rotatably supported.Also rigidly attached to the main frame of the pulley block is a guidemember 26 which serves to support a resilient'ly mounted chain anchoringdevice 27 the latter being provided with a rod 28 which is slidablyjournalled within the member 26 and with a spring 29. A possibleposition for the parts constituting the chain anchoring means is alsoindicated in dotted lines in FIGURE 1.

The load chain which is designated by 30 is anchored to the device 27and normally either hangs slackly between said device and the sprocketor rests in a chain collecting bucket not shown.

During normal operation of the pulley block there will be slack chainbetween the anchoring device 27 and the sprocket 10 and said chain willbe out of contact with the bobbin like member 25. At this stage theslide member Ztl will be maintained in the lowermost position by thespring 22 and the pawl 18 will be displaced to the right out ofengagement with the recess 17 in the sprocket so that the latter will befree to rotate in a clockwise direction as shown in the drawing. As loadhook approaches its uily lowered position, the amount of slack chainbetween the anchoring device 27 and the sprocket 10 will decreaseprogressively to such an extent that said chain will engage the bobbinlike member 25 and will force the member 20 upwardly against the actionof its spring 22 until the position illustrated in the drawing isattained. In this position, the pawl 18 will have been moved intoengagement with the recess 17 in the sprocket 16 and will thuspositively lock the latter against further rotation in the direction tocause Vfurther lowering of the load hook. The resilient mounting of theanchoring device 27 will ensure that the load on that portion of thechain between the sprocket 10 and said device will be very small whenthe sprocket is so locked.

It will be appreciated that by forming the sprocket with a furtherrecess which is similar to the recess 17 it is possible to provide apawl somewhat similar to the pawl 18 and adapted to limit the travel ofthe chain in the upwards direction. A possible arrangement isillustrated in FIG- URE 3 wherein the load sprocket 10 is provided witha recess 31 with which. a pawl 32 is adapted to cooperate. The pawl issupported for sliding movement in suitable guides 33 and is normallyurged into an inoperative position shown in dotted lines by means of aspring 34. The chain 30 is arranged to pass through a slot or aperturein the pawl 32 and the arrangement is such that during a normal liftingor lowering motion of the chain said pawl will be maintained in itsinoperative or off position. However during a lifting operation when thechain approaches the upward limit of its travel, the block normallysupporting the load hook or other load supporting means will contact thepawl 32 and move the same against the action of the spring 34 into itsoperative or engaged position as shown in full lines thereby positivelyto lock. the sprocket 10. In FIGURE 3 the aforesaid block is indicateddiagrammatically at 35. The spring 34 will effectively serve to minimizethe shock to the load chain which would otherwise occur, when the loadchain reaches its highest position. The magnitude of such a shock wouldof course be related to the setting of the slipping clutch between, thesprocket 10 and the drive motor of the hoist.

An arrangement such as is shown in FIGURE 3 could well be adapted forlimiting downward travel of the chain rather than the mechanism shown inFIGURE 2.

In the foregoing, reference has been made solely to the application ofthe invention to electrically operated chain pulley blocks but in factthe mechanism above described could readily be adapted for use with anelectrically operated wire rope pulley block wherein the wire or cableis wound on a drum such cable serving to support a bottom pulley blockcarrying the load hook. With such wire rope pulley blocks, it is commonpractice to employ a rope guide which is adapted to move axially of thedrum in one direction or the other depending upon whether the rope isbeing wound on or ofi the drum. Such a rope guide could be employed tooperate pawls arranged to engage the drum when the bottom block was ateither of its two extremes of travel. In other words as the bottom blockapproached one extreme position which would also correspond with therope guide approaching one limiting position, a rope guide would actuatethe pawl to lock the drum while as the bottom block approached its otherextreme position with consequent approach of said guide to its otherextreme position said guide would then actuate the second pawl to againlock said drum. The introduction of such pawls would result in a markedimprovement in operation of such a pulley block, since:

(i) When lifting, the bottom block can be stopped just clear of the wirerope guide so that it will not, as has happened heretofore, hit the ropeguide or the drum.

(2) On lowering when reaching the extremity of downward travel the pawlmay be caused to engage the drum while the statutory two dead turns arestill wound on said drum. Heretofore this condition (i.e. the presenceof the two dead turns) has been ensured by switching off the motor andapplying the brake but with the arrangement now envisaged such anelectrical control may be eliminated.

It will be appreciated that should the bottom block not be required totravel to the very highest or very lowest positions, intermediatestopping points would readily be arranged simply by adjusting the meanscontrolled by the wire rope guide in order that the pawls would beactuated earlier in the axial travel of said guide i.e. before thelatter approached either of its extreme positions.

I claim:

1. In a chain hoist wherein a chain is anchored at one end to a hoistbody and passes over a chain sprocket which is driven by an electricmotor through the intermediary of a slipping clutch, an improvementcomprising two pawl devices each movable into and out of an operativeposition wherein it Will lock the chain sprocket against rotation, anactuating member movable between first and second positions and engagingone of said pawl devices to effect movement thereof between inoperativeand operative positions coresponcling to the first and second positionsof said actuating member, resilient means acting on said actuatingmember to urge the same into its first position, means associated withsaid actuating member so that as the chain approaches the lower limit ofits travel, that portion of the chain between the sprocket and theanchor point will be effective to cause displacement of the actuatingmember to its second position with resultant movement of said one pawldevice into its operative position, resilient means associated with thesecond pawl device and normally effective to maintain the same in aninoperative position, and means including an abutment carried by saidchain for contacting said second pawl device to move the same againstthe action of the associated resilient means into its operative positionas the chain approaches the upper limit.

2. The improvement as claimed in claim 1 comprising means resilientlyanchoring said one end of the chain to the hoist body.

3. The improvement as claimed in claim 1 wherein said one pawl device isprovided with an angled slot, said actuating member extending throughsaid angled slot and being slidable in said slot between said iirst andsecond positions, said actuating member including an angled portionwhich engages said one pawl device in the angled slot thereof to movesaid one pawl device between the inoperative and operative positions asthe actuating member is moved back and forth between said first andsecond positions.

References Cited UNITED STATES PATENTS 2,053,976 9/1936 Stahl 254--1733,261,589 7/1966 Neumeier 254-173 3,290,012 12/1966 Matthews 254-187FOREIGN PATENTS 1,116,364 11/1961 Germany.

EVON C. BLUNK, Primary Examiner.

H. C. HORNSBY, Assistant Examiner.

